1. Field of the Invention
This invention relates to the structural arrangement of a very compact flash device for a camera.
2. Description of the Related Art
The conventional electronic flash unit has been arranged as follows: A flash discharge tube which is formed with a rare gas such as xenon sealed in a glass tube of a circular sectional shape. Cathode and anode electrodes are disposed at two ends of a cylindrical straight glass tube. A transparent conductive coat mainly consisting of tin oxide is applied to the peripheral surface of the straight glass tube at a part between the fore ends of the anode and cathode electrodes disposed within the glass tube to form a trigger electrode. The trigger electrode has a lead wire which is formed by winding a fine nickel wire or the like round the part of the glass tube where the transparent conductive coat is applied.
In arranging the the above stated flash tube in an electronic flash unit, the flash tube is provided with a reflector for efficient irradiation within a given range. The reflector is formed into a concave shape approximately having a surface of revolution at least relative to the optical axis of the flash tube. The flash tube is located either at or in the neighborhood of the focal point within the flash tube.
The body of the reflector within which the flash tube is disposed is made of either a synthetic resin material with aluminum applied to the surface thereof by vacuum evaporation or a brightening aluminum alloy plate with its surface specularly finished. The reflector is in a shape consisting of a pair of reflecting planes on its longer sides extending in parallel to the flash tube and a pair of reflection planes extending on its shorter sides perpendicularly to the flash tube. With the reflector arranged in this manner, however, the illuminating light distribution characteristic of the reflection plane on the shorter side is inferior to that of the reflection plane on the longer side. In other words, the light utilization rate (or yield) of the flash device is inadequate. To solve this problem, there has been known a method in which the shape of the reflector is changed to increase the front width and to deepen the depth thereof. However, this method has resulted in an increased size of the electronic flash unit.